It has been recognized that a jet of liquid emitted though a nozzle, particularly a nozzle having a small orifice, will cut or, more properly erode, hard substances such as stone if the velocity is high enough.
A typical example of prior art is to be found in U.S. Pat. No. 4,111,490, to D. J. LIESVELD, which discloses, inter alia, apparatus for the channel cutting of hard materials using high-velocity fluid jets. U.S. Pat. No 4,111,490 teaches the use of a water lance having a nozzle which, "preferably is held fixed for each channel cut pass but can be oscillated in a direction normal to the material surface while being moved along a line spaced from but parallel to the surface of material to be cut." The entire apparatus moves along rails which are laid on the surface of the work surface and, after a channel cut has been completed, the nozzle assembly is lowered and a deeper channel cut line is eroded until the required or desired cutting depth has been attained. The lance itself is unsupported, however and thus may well be "whippy" although the specification is silent on this point. With such a whippy, unsupported lance the depth of cut possible is limited since the lance becomes unstable. Moreover, more oscillation of the cutting head cannot provide optimal conditions for the winning of blocks of stone from, say, a natural outcrop of the material to be won.
Other, and perhaps less relevant, examples of prior art apparatus are to be found in:
1) Australian Patent No. 543913, by DRAVO CORPORATION; PA0 2) Australian Patent No. 567396, by CHARLES LOEGEL JNR; PA0 3) Australian Patent Application No 66411/86 by TADOLE PTY LTD; PA0 4) U.K. Patent No. 1460711, by PRESSURE DYNAMICS LTD; PA0 5) U.S. Pat. No. 3,857,516, by N. S. H. TAYLOR et al; PA0 6) U.S. Pat. No. 3,960,407, by C. A. NOREN; PA0 7) U.S. Pat. No. 3,796,371, by N. S. H. TAYLOR et al; PA0 8) U.S. Pat. No. 4,240,664, by A. MAHYERA; and PA0 9) U.S. Pat. No. 4,367,902, by K. H. SCHWARTING et al.